One of the principal routs to the production of ethylene involves cracking ethane at high temperatures. Purified ethane obtained from refinery gas streams or from natural gas is heated to temperatures of about 816° C. The thermal cracking, which takes place without a catalyst involves free radicals and a chain reaction.
The results of the thermal cracking depend on such variables as temperature, pressure and residence time, collectively referred to as cracking severity. Even under the best of conditions, numerous byproducts limit the production of ethylene. Thus, a representative yield of ethylene is about 80 percent.
Because of the formation of byproducts ranging from hydrogen and methane to butane and higher molecular weight hydrocarbons, extensive processing is needed to separate the ethylene product. This requirement is made more stringent because many of the uses of ethylene, for example, polyethylene production, demand high purity material.
For the above reasons, present know-how for producing ethylene from ethane has severe drawbacks. Capital investment is substantial and operating efficiencies are average.